What a Certificate of Analysis Actually Is
A Certificate of Analysis (CoA) is a document issued by an independent testing laboratory confirming what's actually inside a specific batch of material — not what the label claims, but what analytical testing has verified. For research peptides, a proper CoA answers two separate questions: is this the compound it claims to be (identity), and how pure is it (purity)?
These are answered by two distinct analytical methods, which is why a legitimate CoA should reference both HPLC and mass spectrometry rather than relying on a single test. A supplier that only provides one type of result is giving you half the picture.
The Key Sections of a CoA
Batch / Lot Number
Every legitimate CoA is tied to a specific production batch, not a general product line. This number should match a corresponding batch number printed on the vial label itself. If a supplier provides a CoA that isn't tied to a specific batch, or where the batch number doesn't match what's on your vial, the document is effectively meaningless — it could be testing data from a completely different production run.
Identity Confirmation (Mass Spectrometry)
Mass spectrometry (MS) confirms that a sample's molecular weight matches the expected molecular weight of the compound in question. A CoA should state the expected molecular weight alongside the observed result. A close match confirms identity — that the vial actually contains the peptide it claims to, rather than a different or degraded compound.
Purity Percentage (HPLC)
High Performance Liquid Chromatography (HPLC) separates a sample into its component parts and measures what proportion is the target peptide versus impurities, degradation products, or synthesis byproducts. This is expressed as a purity percentage — research-grade peptides are typically expected to test above 98%.
Testing Date & Laboratory
A proper CoA states when testing was performed and, ideally, names or identifies the testing laboratory. Peptides degrade over time, so a CoA from testing performed long before a batch was sold is less meaningful than one performed close to production. An independent third-party lab (rather than in-house testing by the seller) adds meaningful credibility, since it removes the conflict of interest of a company grading its own product.
Reading a Chromatogram
Many CoAs include a chromatogram image — a graph showing peaks plotted against retention time. For a non-specialist, the key thing to look for is a single large, sharp, dominant peak. This represents the target peptide. Smaller peaks elsewhere on the graph represent impurities or byproducts.
Red Flags: Signs of a Fake or Weak CoA
- A CoA with no batch number, or a batch number that doesn't match the vial
- Only one type of test result (e.g. purity but no identity confirmation, or vice versa)
- No named or identifiable testing laboratory — anonymous or unverifiable sourcing
- A testing date far removed from the batch's actual production or sale date
- Identical CoAs reused across completely different batches — a sign the document may not reflect actual per-batch testing
- A chromatogram image that looks inconsistent with the stated purity percentage
Why This Matters for Research Reproducibility
Research findings are only as reliable as the materials used to produce them. A peptide with unknown or misrepresented purity introduces an uncontrolled variable into any protocol it's used in — results can vary batch to batch for reasons that have nothing to do with the research question being studied. Requesting and actually reviewing a CoA — not just checking that one exists — is a basic step in maintaining research integrity.
What to Look For in a Testing Laboratory
Not all third-party labs offer the same level of rigour. A few practical markers of a credible testing laboratory:
- Accreditation to a recognised quality standard (such as ISO/IEC 17025), which governs testing laboratory competence generally
- A named, verifiable laboratory rather than an anonymous or unnamed "independent lab"
- Consistent methodology disclosed across CoAs — the same testing approach applied batch to batch, rather than different methods each time
- Willingness to provide the underlying chromatogram or spectral data, not just a final summary percentage
A supplier's willingness to provide this information, and to answer direct questions about which lab performed testing and when, is itself a useful signal — reputable suppliers are generally comfortable being transparent about their testing process, while suppliers relying on unverifiable documentation tend to be evasive about specifics.
Frequently Asked Questions
Can a CoA be faked?
Yes. Because a CoA is simply a document, nothing technically prevents a bad-faith supplier from fabricating one, reusing an old result across different batches, or editing a legitimate CoA template with false figures. This is exactly why matching the batch number on the document to the batch number on the vial, and checking for a named, verifiable testing lab, matters more than the final percentage figure itself.
What purity percentage should research-grade peptide meet?
Conventions vary by field and application, but ≥98% is a commonly cited threshold for research-grade material. Purity below this doesn't necessarily make a peptide unusable for every purpose, but any protocol sensitive to exact concentration should account for the actual tested purity rather than assuming the label figure applies universally.
Should every batch have its own CoA, or is one document enough for a whole product line?
Every batch should have its own CoA, since purity and identity can vary between production runs even for the same nominal product. A single CoA reused indefinitely across many different batches is a red flag rather than a convenience.
What should I do if a supplier refuses to provide a CoA on request?
Treat this as a significant warning sign. Legitimate research suppliers generally expect this question and should be able to provide batch-specific documentation without hesitation. A refusal, vague deflection, or an offer to provide "general" testing data unrelated to your specific batch all suggest the supplier either doesn't test individual batches or doesn't want that testing scrutinised.